The present invention generally relates to an apparatus and method for detecting a depolarization activation wave (R wave) of the heart. The present invention is more particularly directed to an atrial defibrillator and method employing such an apparatus and method for reliably detecting a depolarization activation wave of the heart and delivering cardioverting electrical energy to the atria of the heart in synchronism with the detected depolarization activation wave.
Atrial fibrillation is probably the most common cardiac arrhythmia. Although it is not usually a life threatening arrhythmia, it is associated with strokes thought to be caused by blood clots forming in areas of stagnant blood flow as a result of prolonged atrial fibrillation. In addition, patients afflicted with atrial fibrillation generally experience palpitations of the heart and may even experience dizziness or even loss of consciousness.
Atrial fibrillation occurs suddenly and many times can only be corrected by a discharge of electrical energy to the heart through the skin of the patient by way of an external defibrillator of the type well known in the art. This treatment is commonly referred to as synchronized cardioversion and, as its name implies, involves applying cardioverting or defibrillating electrical energy to the heart in synchronism with a detected depolarization activation wave (R wave) of the heart. The treatment is very painful and, unfortunately, most often only results in temporary relief for patients, lasting but a few weeks.
Drugs are available for reducing the incidence of atrial fibrillation. However, these drugs have many side effects and many patients are resistant to them which greatly reduces their therapeutic effect.
Implantable atrial defibrillators have been proposed to provide patients suffering from occurrences of atrial fibrillation with relief. Unfortunately, date, none of these atrial defibrillators have become a commercial realty to the detriment of such patients.
Implantable atrial defibrillators proposed in the past have exhibited a number of disadvantages which probably have been the cause of these defibrillators from becoming a commercial reality. Two such defibrillators, although represented as being implantable, were not fully automatic, requiring human interaction for cardioverting or defibrillating the heart. Both of these defibrillators require the patient to recognize the symptoms of atrial fibrillation with one defibrillator requiring a visit to a physician to activate the defibrillator and the other defibrillator requiring the patient to activate the defibrillator from external to the patient's skin with a magnet.
Synchronizing the delivery of the defibrillating or cardioverting electrical energy with a depolarization activation wave (R wave) of the heart important to prevent ventricular fibrillation. Ventricular fibrillation is a fatal arrhythmia which can be caused by electrical energy being delivered to the heart at the wrong time in the cardiac cycle, such during the T wave of the cycle. As a result, it is most desirable to sense depolarization activation waves of the heart to generate synchronization pulses (or signals) a manner which avoids detecting noise as a depolarization activation wave. Unfortunately, until recently, implantable atrial defibrillators which have been proposed have not provided either such noise immunity any other means for assuring reliable synchronization.
One recently proposed atrial defibrillator which does provide reliable and noise immune detection of depolarization activation waves of the heart and delivery of electrical cardioverting or defibrillating electrical energy to the atria of the heart in synchronism with a detected depolarization activation wave is fully described in copending U.S. application Ser. No. 07/685,130 filed Apr. 12, 1991, in the names John M. Adams and Clifton A. Alferness and entitled ATRIAL DEFIBRILLATOR AND METHOD, which application assigned to the assignee of the present invention and incorporated herein by reference. The atrial defibrillator there disclosed includes first means sensing depolarization activation waves at a first of the heart and second means for sensing the depolarization activation waves at a second area of the heart. The atrial defibrillator further includes detector for detecting non-coincident sensing cf depolarization activation wave at the first area of the heart by the first sensing means and at the second area of the heart by the second sensing means. The atrial defibrillator further includes storage means for storing electrical energy and delivery means coupled to the storage means and being responsive to the non-coincident sensing of a depolarization activation wave at the first and second areas of the heart for applying predetermined amount of stored electrical energy to the atria for cardioverting or defibrillating the heart. Reliable and noise immune detection of the depolarization activation waves is provided by the non-coincident sensing of the depolarization activation waves which would be mistaken for a depolarization activation wave by prior atrial defibrillators is not mistaken a depolarization activation wave because such noise would be sensed coincidently by the first and second sensing means at the first and second areas of the heart. Hence, by the non-coincident sensing of the depolarization activation waves and the non-coincident detection thereof by the detector, the above atrial defibrillator capable of reliably detecting depolarization activation waves in a manner which is immune to noise. The apparatus and method of the present invention represents an alternative approach to reliable detection of depolarization activation waves of the heart and the delivery of electrical cardioverting energy to the atria of the heart in synchronism with a detected depolarization activation wave.